Fix opening sidebar/popup URL of other extensions instead of tab.url

[ariasuni]

Someone reported that this extension doesn’t work from Tab Center Reborn. I can reproduce with Tree Style Tab, too.

Indeed, when your extension is used from a context menu invoked from another extension, it didn’t check for tab.url first, and instead found the page URL, in this case the URL of the panel or popup. Now it checks for tab.url first, then try to find the URL like before.

[darktrojan]

Thanks for your patch! I've confused Github with it somehow, so closing this pull manually.

[ariasuni]

Nice!